As is called a ubiquitous information society, in recent years, an environment has been managed so that one can access the information network whenever and wherever he/she likes. In such an environment, an individual authentication technique is attracting attentions, such that an ID (identification number) is assigned to each object, thereby the history of the object is clarified and the manufacturing, management, or the like is facilitated. In particular, a semiconductor device which can transmit and receive data through wireless communication (hereinafter also called a wireless tag) has started to be used.
FIG. 3A shows an example of a wireless communication system using a wireless tag. The wireless communication system is formed of a reader/writer 300, a control terminal 302, and a wireless tag 303. The control terminal 302 controls the reader/writer 300. Data is transmitted and received wirelessly between an antenna 301 connected to the reader/writer 300 and an antenna 304 in the wireless tag 303.
Wireless data transmission and reception are performed as follows. The antenna 304 in the wireless tag 303 receives a wireless signal outputted from the antenna 301 connected to the reader/writer 300. The wireless signal is an electromagnetic wave which is modulated in accordance with the data to be transmitted. The electromagnetic wave for transmitting data is called a carrier wave. A wireless signal is also called a carrier wave which is modulated in accordance with data. A wireless signal (a modulated carrier wave 330) is received by the antenna 304 and inputted to a signal processing circuit 305 in the wireless tag 303 to be processed. In this manner, the wireless tag 303 obtains data contained in the wireless signal (the modulated carrier wave 330). Subsequently, a signal containing response data is outputted from the signal processing circuit 305. The antenna 304 in the wireless tag 303 transmits a wireless signal (the modulated carrier wave 330) corresponding to the outputted signal to the antenna 301 connected to the reader/writer 300. The wireless signal (the modulated carrier wave 330) is received by the antenna 301 and the reader/writer 300 obtains the response data and accumulates the response data in the control terminal 302.
The antenna 304 in the wireless tag 303 receiving a wireless signal (the modulated carrier wave 330) outputted from the antenna 301 connected to the reader/writer 300, the wireless signal (the modulated carrier wave 330) is inputted through a band-pass filter 306 to a power source circuit 307 in the wireless tag 303. The power source circuit 307 generates a power source voltage for driving an internal circuit (corresponding to the signal processing circuit 305 or the like) in the wireless tag 303 from the inputted wireless signal (the modulated carrier wave 330).
In specific, the power source circuit 307 includes a rectifying circuit 308 which converts the inputted wireless signal (the modulated carrier wave 330) into a DC signal, and a holding capacitor 309 which smoothes the DC signal. In this manner, the power source circuit 307 generates a DC voltage between a first terminal 310 and a second terminal 311. The generated DC voltage is supplied as a power source voltage to an internal circuit of the wireless tag 303.
A wireless tag which generates a power source voltage for driving an internal circuit by using a wireless signal (the modulated carrier wave 330) as described above is disclosed in, for example, Patent Document 1.
[Patent Document 1]
Japanese Patent Laid-open No. 2002-319007